This invention relates to an institutional washing process in which a soil release polymer is used in a separate pretreatment step.
Besides the ingredients essential to the washing process, such as surfactants and builders, detergents generally contain other constituents which may be collectively referred to as washing auxiliaries and which comprise such diverse groups of active substances as foam regulators, redeposition inhibitors, bleaching agents, bleach activators and dye transfer inhibitors. Auxiliaries of the type in question also include substances which provide the fibers with soil-repellent properties and which, if present during the washing process, support the soil release capacity of the other detergent ingredients. The same also applies to cleaning compositions for hard surfaces. Substances such as these are often referred to as soil release agents or, by virtue of their ability to provide the treated surface, for example the fibers, with soil-repellent properties, as soil repellents. By virtue of their chemical similarity to polyester fibers, copolyesters containing dicarboxylic acid units, alkylene glycol units and polyalkylene glycol units are particularly effective soil release agents. However, copolyesters are also capable of developing the required effect in non-polyester fabrics. Soil release copolyesters of the type mentioned and their use in detergents have been known for some time.
Thus, DE-OS 16 17 141 describes a washing process using polyethylene terephthalate/polyoxyethylene glycol copolymers. DE-OS 22 00 911 relates to detergents containing a nonionic surfactant and a copolymer of polyoxyethylene glycol and polyethylene terephthalate. DE-OS 22 53 063 mentions acidic textile finishes containing a copolymer of a dibasic carboxylic acid and an alkylene or cycloalkylene polyglycol and, optionally, an alkylene or cycloalkylene glycol. According to DE-OS 33 24 258, ethylene terephthalate/polyethylene oxide terephthalate polymers with molecular weights of 15,000 to 50,000, in which the polyethylene glycol units have molecular weights of 1,000 to 10,000 and the molar ratio of ethylene terephthalate to polyethylene oxide terephthalate is 2:1 to 6:1, may be used in detergents. European patent EP 066 944 relates to fabric treatment compositions containing a copolyester of ethylene glycol, polyethylene glycol, aromatic dicarboxylic acid and sulfonated aromatic dicarboxylic acid in certain molar ratios. European patent EP 185 427 mentions methyl-terminated or ethyl-terminated polyesters containing ethylene and/or propylene terephthalate and polyethylene oxide terephthalate units and detergents containing this soil release polymer. European patent EP 241 984 relates to polyesters which contain substituted ethylene units and glycerol units in addition to oxyethylene groups and terephthalic acid units. European patent EP 241 985 discloses polyesters which, in addition to oxyethylene groups and terephthalic acid units, contain 1,2-propylene, 1,2-butylene and/or 3-methoxy-1,2-propylene groups and glycerol units and which are terminated by C.sub.1-4 alkyl groups. European patent EP 253 567 relates to soil release polymers with a molecular weight of 900 to 9,000 of ethylene terephthalate and polyethylene oxide terephthalate, the polyethylene glycol units having molecular weights of 300 to 3,000 and the molar ratio of ethylene terephthalate to polyethylene oxide terephthalate being 0.6 to 0.95:1. Polyesters containing polypropylene terephthalate and polyoxyethylene terephthalate units which are at least partly terminated by C.sub.1-4 alkyl or acyl groups are known from European patent application EP 272 033. European patent EP 274 907 describes sulfoethyl-terminated terephthalate-containing soil release polyesters. According to European patent application EP 357 280, soil release polymers containing terephthalate, alkylene glycol and poly-C.sub.2-4 -glycol units are prepared by sulfonation of unsaturated terminal groups. Polymers of ethylene terephthalate and polyethylene oxide terephthalate, in which the polyethylene glycol units have molecular weights of 750 to 5,000 and the molar ratio of ethylene terephthalate to polyethylene oxide terephthalate is 50:50 to 90:10 and their use in detergents is described in German patent DE 28 57 292. German patent DE 28 46 984 discloses certain hydrophilic polyurethanes and copolyesters containing recurring alkoyl terephthalate and polyalkoyl terephthalate units and mixtures thereof as anti-soil detergent ingredients. Detergents containing 0.1 to 3% by weight of soil-releasing alkyl cellulose ethers, hydroxyalkyl cellulose ethers or hydroxyalkyl alkyl cellulose ethers are described in German patent DE 26 13 791.
However, all the documents mentioned above relate to detergents for domestic washing. The conditions typical of domestic washing, more particularly the action times of the wash liquor on the laundry to be cleaned of at least 30 minutes and the relatively low alkalinity of the washing liquor of, generally, well below pH 10, differ considerably from those typically prevailing in institutional laundries. Here, the total time taken by the laundry to pass through the continuous batch washing machine with the treatment steps of wetting, prewashing, main washing, rinsing and optionally neutralization is only about 20 to 40 minutes, a period of only a few minutes being allocated for the actual washing process in the main wash zone. Another factor to be taken into account is that, in institutional laundries, the washing is normally much more heavily soiled than in the domestic sector. In order to obtain a satisfactory washing result under these conditions, washing in institutional laundries is normally carried out at far higher pH values than washing in the home. Another difference in relation to domestic detergents is that detergents for institutional washing often contain neither bleaching agent nor bleach activator because, in institutional washing, bleaching and disinfection can be carried out in a separate step, normally in one of the last zones before leaving the continuous batch washing machine.
International patent application WO 96/24657 relates to a highly alkaline detergent for use in institutional laundries which contains the above-mentioned soil release polymer and which leads to a significant improvement in cleaning performance when used in the main wash cycle of institutional washing processes.
It has surprisingly been found that cleaning performance in institutional laundries can be distinctly improved if the soil release polymer, in addition to or instead of being used in the actual detergent, is used in a separate pretreatment step.
Accordingly, the present invention relates to the use of soil release polymer in the soaking or prewash step of institutional washing processes.
The general principles of conventional institutional washing processes are described briefly in the following. A detailed account can be found, for example, in the article by H. Kra.beta.mann and H. G. Hloch entitled "Waschverfahren in der Gewerblichen Wascherei (Institutional Washing Processes)", Tenside Surfactants Detergents 24 (1987), 341-349 and the literature cited therein.
Institutional washing processes differ from domestic washing processes inter alia in the fact that, although various types of fabrics and differently soiled fabrics have to be washed, the bulk of the laundry within the material sent for washing is normally the same so that a washing technique specially adapted to the particular cleaning function can be applied. However, there is a greater need for high-performance cleaning processes in institutional washing than in domestic washing because heavily soiled laundry, for example oil- and pigment-soiled working apparel, can accumulate.
In order to keep the consumption of detergent as low as possible, the water used for institutional washing is almost always free from hardness ions.
Whereas domestic washing is carried out almost exclusively in liquor-changing drum-type washing machines, various standard processes exist in institutional laundries. Thus, normal domestic washing with liquor-hanging washer-extractors can also be applied to the institutional sector. In these washer-extractors, the washing is successively exposed to various washing and rinsing conditions in a drum, the used liquor leaving the drum on completion of the particular wash phase. The individual steps are made up of soaking, prewashing, main washing, rinsing and spinning or pressing.
So-called continuous batch washing machines, which consist of several successive washing compartments or of a single washing compartment divided by partitions into several sections or chambers, are generally superior to this discontinuous process by virtue of the normally higher throughput of laundry. In continuous batch washing machines, the individual washing steps take place in various zones of the machine through which the laundry passes under program control. Continuous batch washing machines can operate either on the bath-changing principle or with stationary baths. Continuous batch washing machines generally operate on the countercurrent principle, fresh water and dirty washing being introduced into the washing process at opposite ends of the washing machine and moving through the washing machine in more or less opposite directions. Fresh water freed from hardness ions enters the rinsing zone through which the laundry passes as the last zone in about 1 to 10 minutes and from which part is delivered to the main wash zone. Another part of the water emanating from the rinsing zone is often used, together with the water accumulating in the pressing zone of the continuous batch washing machine, for the first step of the washing process, namely wetting of the dry soiled laundry and introduction into the first bath of the continuous batch washing machine. After automatic addition of one or more detergents, the soiled laundry is normally prewashed at 35 to 45.degree. C. and, after a predetermined time, is automatically further transported. The prewash step may also be carried out in several successive units. The used water normally leaves the continuous batch washing machine at the end of the prewash zone. After leaving the prewash zone, the laundry enters the main wash zone which generally consists of several units, often more than ten in number. Because the countercurrent of the water flow is superimposed on the intermittent co-current emanating from transport of the laundry, which results in complicated concentration conditions, the main wash detergent is generally not added in the first unit, but in one of the middle units. Bleaching agents, for example hydrogen peroxide or peracetic acid, are normally added in this zone. Also in this zone, the laundry is automatically further transported into the next unit, normally after freely programmable cycle times. In the course of the final rinsing step, the laundry is normally neutralized ("acidified") by automatically dosed addition of organic acids to the aqueous rinsing solution. Neutralization is essential on account of the use of soft water in conjunction with the alkaline cleaning baths of the main washing step.